1. Field of the Invention
The present invention relates to a composition for a ceramic substrate and a substrate prepared from the composition. More particularly, the present invention relates to a composition which can be sintered at a low temperature of not higher than 1,000.degree. C. in a non-oxidizing atmosphere, and a substrate prepared from such a composition.
2. Discussion of Background
Electronic devices are known which are prepared by printing a conductive paste in predetermined patterns on green sheets of glass ceramic and laminating a plurality of such printed green sheets, followed by sintering to form a multi-layer circuit board or substrate. In such electronic devices, the conductive connection between the respective conductive layers is established either by printing a conductive paste in viaholes preliminarily formed in the green sheets or by filling a conductive substance in such via holes.
As such a conductive paste, a Au paste, a Ag-Pd paste and a Cu paste are known. However, the Au paste has a drawback that it is expensive. The Ag-Pd paste has a drawback that the electrical resistance is high, and the electrical migration tends to appear. The Cu paste has merits such that the electrical resistance is low, and the electrical migration of the formed conductor does not tend to appear, and it is hardly corroded by soldering. However, copper is susceptible to oxidation. In order to avoid the oxidation, the sintering for the formation of the conductor is usually conducted in a nitrogen atmosphere having an oxygen concentration of not higher than 10 ppm.
The following compositions have been known, whereby an organic binder in the green sheets can be removed by sintering them in such a non-oxidizing atmosphere.
Japanese Unexamined Patent Publication No. 36363/1985 discloses a composition comprising glass powder containing SiO.sub.2, Al.sub.2 O.sub.3, MgO, BaO, B2O.sub.3 and Bi.sub.2 O.sub.3, and an oxidizing agent added thereto. Japanese Unexamined Patent Publication No. 38882/1980 discloses a composition comprising glass powder containing SiO.sub.2, Al.sub.2 O.sub.3, ZnO, CaO, SrO and B.sub.2 O.sub.3, and an oxidizing agent. Further, West German Pat. No. 2,755,935 discloses a composition containing SiO.sub.2, Al.sub.2 O.sub.3, ZnO, CaO, SrO and B.sub.2 O.sub.3. However, in each case, when the composition is sintered in a non-oxidizing atmosphere, the removal of the organic binder in the composition is inadequate, and carbon remains, whereby the electrical properties such as the breakdown voltage and the dielectric constant, are poor.